The invention relates generally to engine systems and more particularly to a technique for reducing pollutant emissions, e.g., Nitrogen Oxide (NOx) emissions, in turbocharged internal combustion engines.
Various types of internal combustion engines are in use for powering vehicles such as locomotives, passenger cars and other equipment. An internal combustion engine may include one or more turbochargers for compressing an intake charge (e.g., atmospheric air), which is supplied to one or more combustion chambers within the engine. Each turbocharger includes a turbine driven by exhaust gases from the engine and a compressor driven by the turbine. Moreover, the compressor receives the atmospheric air to be compressed and provides the compressed air to the combustion chambers.
Typically, a turbocharged internal combustion engine is operated such that the intake manifold pressure is higher than the exhaust manifold pressure in the engine. In certain traditional systems, exhaust gas recirculation (EGR) is employed for reducing undesirable NOx emissions in operation of the engines. Unfortunately, it is difficult to control the exhaust gas recirculation of the exhaust gases while substantially overcoming the pressure difference between the intake and exhaust manifolds. Further, such techniques substantially impact the specific fuel consumption (SFC) and particulate matter (PM) emissions and do not provide efficient control of the exhaust gas circulation for the entire range of throttle notch settings applied to the duty cycle for locomotive operation and at high altitudes.
Accordingly, a need exists for providing a turbocharged engine system that has substantially reduced NOx emissions for different engine operating conditions while achieving a desired specific fuel consumption (SFC) for the engine.